This invention relates to the construction of a lens suitable for use with millimeter wave electromagnetic radiation for focussing an incoming wave upon a feed horn of an antenna and, more particularly, to the construction of the lens of plural dielectrically loaded waveguides.
Lenses are often utilized in optical systems to focus radiant energy upon a detector or a receptor of the radiant energy. The most frequent situation of such focussing of radiant energy is that of optical systems operating in the visible portion of the electromagnetic spectrum, such optical systems including by way of example, a camera and a television vidicon. Such focussing can be done also at infrared frequencies by use of suitable material for construction of the lens, and also at microwave frequencies by use of a material, such as a ceramic, transparent to radiation at the microwave frequencies.
One aspect in the design of a lens is the aperture of the lens which establishes, in terms of a spherical angle of admittance of incident radiation, an amount of radiation that can be captured by the lens and focussed upon the receptor. The aperture is often described in terms of the ratio of lens focal length to lens diameter, a smaller ratio providing for a larger aperture. In terms of the usual mode of construction of a such a lens, the lens has convex optical surfaces, wherein for a collimated beam of incident radiation, the receptor is located behind the lens at a distance equal to the focal length. Increasing the diameter of the lens increases the aperture, but only to the point wherein the aperture size is constrained by limitations of geometric optics and available lens materials of suitably large dielectric constant.
In a system of communication of microwave signals such as millimeter wave microwave signals, of particular interest herein, the microwave signal may propagate through a waveguide having cross-sectional dimensions much greater than the cross-sectional dimensions of a receptor of the microwave signal. A wide aperture lens would be useful in directing the microwave radiation to the receptor to insure that all available radiant power is received. This avoids loss of power which would decrease the available signal-to-noise power ratio and, therefore, impair the quality of signal reception. A problem arises in that available lens construction does not allow for as large a lens aperture as would be desired.